The state of the art is familiar with several concepts for making available motorised and non-motorised aircraft with flapping wings.
However, so far there have only been reports of a few successful attempts. In 1942, Adalbert Schmid succeeded in taking off with a motor-driven device and in flying it a short distance. In 2006, a motor-driven ornithopter flown by Prof. James De Laurier managed to fly about 300 meters. In addition, he made use of a booster turbine for extra speed. One feature that both machines had in common was a pair of fixed auxiliary wings that gave continuous uplift in the right flow conditions, and a pair of flapping wings that provided for the acceleration.
It is hard to say how successful Emil Hartmann was with his flapping-wing flight in 1960, as it was propelled forwards by a rubber band that was used to start the flight and then to continue it with the aid of a pair of flapping wings. The power required for the flapping of the wings was provided by the arms of the pilot by means of levers and baffle plates.
The muscle power that a pilot may summon up with his arms alone in order to operate the flapping wings is probably not sufficient in order to successfully imitate the prolonged flapping motion of a bird in flight. Accordingly, other prior-art aircraft envisage using the pilot's leg movement to drive the flapping wings. For example, one elaborate method of turning leg motion into flapping wing motion is described in German patent specification DE 35 37 365 C2.
Other proposals for muscle-powered ornithopters, such as are described in the German patent specifications DE 19 50 970 074 A1 and DE 29 09 975 A1, envisage the application of force by means of mass acceleration of the body of the pilot. However, these concepts ignore the complicated sequence of motion that is necessary in order to successfully imitate the flight of a bird. Furthermore, these concepts also ignore the important role that the position of the elevator unit plays in the different phases of the flapping of the main wings.
The latter publications describe rigid wings that are straight in two planes, and which may only perform a two-dimensional flapping motion because they are mounted on a rotational axis. By way of contrast, the wings of birds describe a kind of rowing motion and during the course of this movement they change portions of their wing profile.
The wing-flapping flight of the bird is facilitated first and foremost by the bird's sequence of motion between the bird's primaries and secondaries. With an up-and-down motion of the wings, the wing performs a rowing movement in its outer region—and with the bird, this corresponds to the primary,—while the section of the wing close to the fuselage—with the bird, this corresponds to the secondary—, keeping much the same angle of adjustment. When in the upward flight phase, the bird adjusts the primary so that it achieves greater uplift. On the other hand, the primary is adjusted negatively during the downward flight phase so that it generates only a slight uplift, or no uplift at all. In this way, the primary can provide the necessary propulsion, while the secondary can ensure constant uplift.